Mileage accumulation dynamometer



4 Sheets-5heet 1` R- HOLLINGHURST MILEAGE ACCUMULATION DYNAMOMETER Aug.l, 1967 Filed June 26. 1964 4 Sheets-Sheet 2 Filed June 2G, 1964w|llrl++||| NSGQ Aug- 1, 1967 R. HOLLINGHURST 3,333,4.63

MI LEAGE ACCUMULAT I ON DYNAMOMETER Filed June 26, 1964 4 Sheets-Sheet 5Aug. l, 1967 Filed June 26, 1964 `R. HOLLINGHURST MILEAGE AGCUMULTIONDYNAMOMETER 4v sheets-snaai 4 United States LPatent O 3,333,463 MELEAGEACCUMULATION DYNAMOMETER Ralph Hoilinghnrst, Glassboro, NJ., assignor toMobil Oil Corporation, New York, N.Y., a corporation of New York FiledJune 26, 1964, Ser. No. 378,395 Claims priority, application GreatBritain, June 27, 1963, 25,526/63 12 Claims. (Cl. 73-117) The presentinvention concerns a method and apparatus for running the engine andassociated power train in a motor vehicle in the same manner as innormal road operation, while maintaining the body of the vehiclestationary, so as to accumulate effective road mileage without thenecessity of using the road.

Various petroleum products used in motor vehicles as fuels andlubricants, and other materials, must be tested with respect to theirperformance, under conditions as` closely similar as possible to thosewhich occur in normal use. Difficulties occur in carrying out tests inmotor vehicles under actual road conditions, due for instance tounpredictable traiiic conditions and variations in the perfomance of thedriver.

To avoid these disadvantages it has already been proposed to operatemotor vehicles for extended periods on a chassis dynamometer apparatusin which engine mileage may be accumulated under pre-arranged conditionsof speed and load while the vehicle remains captive. We refer to suchapparatus herein as a mileage accumulator dynamometer. It has also beenproposed to operate such a dynamometer apparatus in response to a codedset of signals according to a program previously compiled or recorded.According to one know proposal, such a program is previously obtained inactual road use of a motor vehicle which serves as a master forsubsequent tests.

Mileage accumulation dynamometers and their uses are described forinstance in Automobile Engineer, April 1958, pages 142 to 145, andAugust 1958, pages 297 to 302, in United Kingdom patent specication No.882,380 and in United States patent specification No. 3,050,994. Thepresent invention is applicable in the employment of mileageaccumulation dynamometers quite broadly and there is no need to describethese in particular detail herein.

A typical mileage accumulation dynamometer installation comprises asolid foundation, for instance of concrete, incorporating a well or pitin which the dynamometer itself is mounted. The lwell is covered by adeck on which the vehicle may stand, the deck being cut away so that thewheels of the vehicle which transmit the drive to the road can bearranged to ride on one or more traction rolls, these rolls beingmounted on a common axle which transmits the wheel power through gearingand shafts to the machinery which simulates highway load conditions,which comprise windage, inertia, rolling friction and gradient (andbraking). Anchoring points are provided so that the automobile or othermotor vehicle may be secured against movement along the ground.

The traction rolls generally drive a centrifugal fan (or the latter maybe wholly or partly powered separately) `the purpose of which is toprovide, through suitable ducting adjusted to fit the size of thevehicle or more particularly its radiator, cooling air at the front ofthe vehicle and past its underbodyprepresenting the cooling effect ofair on the road. The fan may also provide a resistance to be overcome bythe engine, equivalent to the effective wind resistance of the motorvehicle. This is necessary because the air impinging on the stationaryvehicle produces no drag on the vehicle engine under test. It is foundin practice that the resistance set up by the 3,333,463 Patented Aug. 1,1967 fan can be arranged to vary in approximately the same manner as theroad wind resistance, as a function of the cube of the speed. Ifdesired, and in any case when the fan is powered separately, appropriatealternative facilities for absorbing a matching amount of power from thetraction rolls, must be made.

Some form of adjustable load is provided as an added drag on thetraction rolls to represent the inertia due to the weight of the motorvehicle, i.e. the resistance to acceleration. This load generally takesthe form of a series of selected flywheel weights proportional to thecar weight and mounted to rotate on the dynamometer shaft, but othermeans, eg. electrical, may be utilized to provide the necessary degreeof inertia. In the event that the inherent inertia of the system exceedsthat of the vehicle under test, motor assistance may be used to reducethe effective inertia.

Vehicle rolling friction is approximated by the inherent frictional dragof the system.

Braking is applied to the traction rolls by means of the dynamometerbrake in which an electric eld is applied to absorb energy derived fromthe rolls. The brake can be adjusted to enable (l) decelerationcorresponding to the use of the car brakes, which are, of course, not ina position to perform their function normally, and (2) load applicationcorresponding to the extra power needed on a gradient. For a givenweight of car, the correct power absorption at a given speed to obtainany desired gradient may be computed. The most convenient dynamometerpossesses a linear speed/power characteristic at a given excitationor'setting, when the simulated gradient obtained becomes independent ofspeed.

The dynamometer is normally equipped with roll locking friction brakesfor use while mounting a vehicle for test, with emergency jacks in caseof tire failure, and with other ancillary devices such as means formeasuring the variation of any desired engine variable such astemperature, manifold vacuum, and the like, and means for controllingambient atmospheric conditions.

Mileage accumulation dynamometers are designed to accommodate the wholerange of vehicle sizes, weights and speeds, with suitable adaptation andproportioning of those components of the system which carry, produce orabsorb loads. Such numerical adaptation forms no part of the presentinvention which is applicable quite generally. Several mileageaccumulation dynamometers are preferably mounted together within thecommand of a common control point.

In one particular known system, the throttle position and braking loadare varied according to a program predetermined by magnetic recording ona tape during a master test in a motor vehicle on the road. The throttleopening during consequent dynamometer tests must then be appropriatelyproportioned for each individual car put under test, to take intoaccount the differences between the characteristics of the throttle andthrottle linkage of each vehicle. This involves standardization at oneparticular road speed and is subject to error at other speeds.

According to further known apparatus the speed and throttle values areboth predetermined according to a road program and a brake signal isused as compensating factor to obtain the correct desired speed for thegiven throttle position.

Variables such as throttle movements, wheel speed and braking actions,may be recorded on magnetic tape during an actual road run, orarbitrarily, by obtaining a voltage dependent on the variable by knownmeans, e.g. with the aid of a potentiometer, and converting the voltagein an oscillator to a frequency modulated signal suited to recording.Such recorded signals may be used to control the appropriate elements ofa chassis dynamometer by separating them from each other first ifnecessary in a discriminator and then converting them back to voltagesignals for actuating dynamometer controls on playback. Such use ofmagnetic tape recordings is known to those skilled in the art and is notdescribed herein in detail. It offers lamong its advantages theavailability of a continuous control signal representing continuous roadbehaviour, capable of frequent cyclic repetition with a high degree ofreproducibility, and a convenient way of storing a variety ofpredetermined programs. One tape output can be -used to control morethan one mileage accumulation dynamometer.

It is the primary object of the present invention to provide a mileageaccumulation dynamometer in which a predetermined wheel speed isobtained reproducibly under given conditions of load, among widelydifferent test vehicles, without the need for compensatory throttleproportioning from vehicle to vehicle.

It is also an object of the invention to provide a dynamometer in whicha predetermined wheel speed is obtained under given conditions of loadaccording to a prearranged program, without the need for a masterprogramming run on the road.

It is a further object of the invention to obtain typical and consistentsimulation of engine behaviour in test runs on a mileage accumulationdynamometer whether from an arbitrary or from a prerecorded program.

It is a yet further object of the invention to provide a mileageaccumulation system in which the wheel speed and Ibraking load are eachspecified according to a predetermined program and the throttle isadjusted automatically as the specified speed is approached so as toprocure test conditions more closely similar than hithertoV adopted, tothose found on the road.

The invention is based on the principle of specifying a predeterminedspeed under given load conditions and controlling the throttle inresponse to the speed attained.

According to the present invention a method of mileage accumulation on achassis dynamometer comprises obtaining a predetermined wheel speed onthe dynamometer under predetermined conditions of load by actuating theengine throttle automatically in response to actual wheel speedachieved. Y

According to the invention, therefore, a mileage accumulationdynamometer comprises one or more traction rolls adapted to be driven bythe engine of a motor vehicle under test through the road wheel orwheels thereof, control means for determining a selected wheel speed inthe rolls, means for applying a predetermined braking load, and controlmeans for adjusting the engine throttle in accordance with actual wheelspeed attained.

The control mean for wheel speed, load and initial throttle opening arepreferably pre-set to vary according to a prepared test program. Thisprogram may be obtained by setting up timed automatic switch gear lorfrom a master tape recording produced on the road, of signalsrepresenting road speed and gradient or braking load. If desired, thegradient or braking signal may be applied manually on the tape, toobviate the use of a torquemeter.

The purpose 'of the throttle control means is to alter the throttleopening in response to the actual wheel speed attained in such a way asto bring that speed to the predetermined value desired, i.e. independence upon the difference between desired and realised speeds. Thethrottle control means is thus analogous to actuation by the driver onthe road and is moreover capable of procuring the desired speeds withoutthe assistance of corrective braking or other interferencewith thedesired predetermined load conditions. The dynamometer system accordingto error signal is developed between the output of a tachometer drivenby the traction rolls, and a reference voltage representing requiredwheel speed, the error signal then being utilized to adjust the throttleposition in relation to the desired wheel speed and subject to feedbackcor- .rections to avoid overshoot.

The invention makes possible the use of one or several test programschosen at will on a wide variety 'of motor vehicles having unequalthrottle characteristics, from a continuous tape recording of speed andload only, or even without a master trip or any trial and errorexperimentation (except to establish windage and frictioncharacteristics). There is no need for throttle proportioning adjustmentsince the throttle is automatically adjusted according to need inobtaining the specified speed, once the throttle actuating means hasbeen accommodated to the span of the throttle opening mechanism of thevehicle, e.g. the pedal.

Any given program may be applied to a wide range of vehicles after me-readjustment of the inertial load in the dynamometer. It is moreover notnecessary to determine the time occupied by acceleration or decelerationunder various conditions, when preparing or recording the program, sincethe system reproduces actual road condi.

tions of itself.

Constant repetition of the same program is possible and a singleoperator can attend to the testing of several vehicles at once if morethan one apparatus according to the invention is provided. The apparatusmay be readily controlled manually, fully automatically by timedswitchgear or from tape, and it may be stopped at any point in theprogram and Vre-set o-r allowed to Iproceed.

Tape operation offers the particular advantage of continuousreproduction of -road circumstances and behaviour as they occur, asopposed to the stepwise program of timed switchgear. Arbitrary programset up on tirned switchgear may be used to produce a taped continuousprogram by recording speed and gradient in a vehicle on the dynamometerof the invention.

Other engine variables of particular interest, such as temperature 'ormanifold vacuum, may also be employed as controlling factors in amileage accumulation dynamometer according to the invention by suitablemodification of the controls, if desired also affecting the throttle.

Timed switch-gear for the provision of a manually compiled program ofcontrol signals for the dynamometer of the present invention forsimulating events o-f real or` imagined road performance, may forinstance take the following form, described by way of illustration.

For each event in a desired sequence of up to, say, 36 events, a set ofcontrols is provided in a unit for the four functions: initial throttleopening, time, road wheel speed, and gradient. A uniselector enables theindividual sets of controls to be brought in to operation in sequenceand provides for cyclic repetition of the whole sequence, which may beshortened to fewer events by setting some of the individual timecontrols at zero.

For each event, the respective set of controls includes a timer, basedon a ramp generator giving linear time controlover an interval of 5minutes. A potentiometer is used to select a desired period from 10seconds to 5 minutes in this interval, after which period a signal ispassed to an additional timer giving up to l1 successive intervals of 5minutes laccording to the setting of a 12- position switch, so that atotal time for each event of from 10 seconds to 'one hour may beselected. At the end of each event, the uniselector is moved on to thenext event and the next unit with a similar set of'controls.

Eachset of controls includes a rotary potentiometer switch tapping off avoltage for maximum throttle opening, as hereinafter explained in moredetail, representing throttle shut to throttle fully open, in incrementsof one-tenth fully open. Setting this switch permits initialacceleration of the engine. Each set of controls includes at least onerotary potentiometer switch tapping olf a voltage representing desiredroad wheel speed, and calibrated as required according to maximum speedand increments of speed desired. Each set of controls may also include afurther rotary switch tapping oi a voltage representing gradient, whichis used to regulate field excitation in the dynamometer proportional tothe required gradient effect, up to a maximum representing full braking,at, say, 150 HP.

The voltages representing throttle maximum setting, desired road wheelspeed and gradient, are fed to the chassis dynamometer apparatus forinstance as described below with reference to the accompanying drawings.

The electronic gear referred to in this description may be obtained, forinstance, from Albert Mann Engineering Ltd., of Basildon, Essex,England.

The invention will now be more fully described, by way of illustrationand without thereby limiting its scope, with reference to theaccompanying drawings, in which:

v FIGURE 1 represents in schematic form the general L layout of amileage accumulation dynamometer according to the invention;

FIGURE 2 represents also in schematic form the circuit for throttlecontrol indicated generally in FIGURE l;

FIGURE 3 represents in graphic form the performance of two cars on amileage accumulation dynamometer (A) of the prior art and (B) accordingto the invention.

The dynamometer shown in FIGURE 1 may, as to its physical layout andprincipal mechanical features, take any of the forms known to the artand is therefore not illustrated herein from a mechanical aspect, but inrelation to the controls associated therewith and the manner of usingthem.

The dynamometer shown in FIGURE l is fed according to circumstances withoperating signals as hereinbefore indicated, derived from timedswitchgear (Auto), lfrom pre-recorded tape (Tape) or from manual settingof controls (Manual). These signals are fed in by lines 1, 2 and 3respectively of an electrical control .panel 4. According to thedisposition of the controls on this selection panel 4, the signals arepassed forward as follows. AU Maximum Throttle signal voltage is passedalong line 5, and a Required Road Speed signal voltage along line 6, toa throttle control circuit shown generally at 7 and more yfullydescribed in relation to FIGURE 2. A Required Gradient signal voltage ispassed along line 18 to a potentiometer 19 referred to as a car weightvernier, whereby the voltage is adjusted in accordance with car weightto allow for its effect in relation to gradient, and then passed in line20 to the gradient/.brake control circuit shown at 16.

' The( throttle control circuit also receives a Road Speed signalrepresenting actual speed attained, from line 17, and a referencevoltage referred to as Comparator Balance Voltage from line 8. Thethrottle control actuates the throttle of the motor vehicle engine 10through a mechanical linkage 9.

The engine 10 drives the road wheels of the vehicle through the usualpower train, shown as a mechanical drive 11, these road wheels beingmounted in driving relationshp on the traction rolls 12 of adynamometer. The main dynamometer shaft 13, transmits the road wheelrotation to several components of the system. Shaft 13 conveys energy tothe fan 21 for blowing cooling air 22 at the engine 10 and rotates anumber of selected iiywheel weights shown generally at 15, to provideinertia corresponding to that of the vehicle. These weights provideincrements of 100 to 200 pounds weight, for instance, in order tosimulate vehicle inertia to within 50 pounds (less than the variation infuel load of common vehicles), and are detachably mounted on the shaft.A tachometer 14 delivers the Road Speed signal already referred to,according to the revolutions of the shaft 13 which drives it. The shaft13 also passes through the gradient appliance, provided for instance byone or more direct ycurrent generators feeding a resistive load, andshown generally at 16. The gradient effect, i.e. the drag on the shaft13, is controlled with the aid of field excitation control through line20,v the excitation voltage being supplied in line 32. Feedback may beapplied fromy the tachometer generator to linearise the gradient effectwith speed. The controlling signal voltage is modified by a factoraccording to vehicle weight, to take into account the fact that theeffect of gradient is a -function of vehicle weight.

Braking is brought about by applying maximum gradient signal and minimumthrottle signal, whereby constant deceleration takes place until atabout l5 miles per hour a friction 'brake may be applied to stop therolls.

Turning now to FIGURE 2, wherein parts common to FIGURE l are indicatedby the same reference numerals, the Maximum Throttle voltage in line 5is seen to be the anode voltage of a thermlionic valve 24 in a cathodefollower circuit. The maximum cathode signal is thus determined by theMaximum Throttle signal. The Required Road Speed signal in line 6 isaccepted by a summing circuit shown at 23, where it is compared with theRoad Speed signal from line 17, to produce a resultant error signal inknown manner in line 25 which is applied to the lgrid of the valve 24.Current ow in valve 24 thus depends on the difference between desiredand achieved road wheel speed and this difference thus determines thesignal in the cathode line 26, subject to the overriding effect of theanode voltage xed by the Maximum Throttle setting. The line 26 feeds acomparator circuit 27 Where the signal in line 26 is compared with acomparator balance voltage originating in line 8 Ifrom a stabilizedsource.

If the signal in line 26 is greater or less than the Icomparator balancevoltage as supplied in line 29, a resultant signal passes to the servoactuation unit 31 to open or close the throttle respectively. The servounit includes the necessary amplifiers to provide power for actuatingthe servo motor in response to the relatively small signals operatingthe circuit. 'Ihe servo motor operates the throttle |by means of asimple arm device, indicated at 9, incorporating a span adjustmentwhereby the full movement of the arm may be matched with the -fullmovement of the throttle linkage. The arm is generally attached to theaccelerator pedal of the vehicle.

The servo motor also actuates a potentiometer 28 in operating thethrottle, whereby the comparator balance voltage is modified. Ihepurpose of this modification is to provide negative feedback so thatthrottle opening is restrained or stopped as required road speed isapproached, lest the actual road speed should overshoot the mark, and toprevent hunting.

The engine under test, and elements 10 to 14 of FIG- URE l, are alsorepresented on FIGURE 2 for complete understanding of the circuit. Itwill be appreciated that the throttle maximum control overrides thespeed control until the opening required in the throttle for the setspeed is less than that already set by the throttle maximum control.

In the operation of the mileage accumulation dynamometer, the motorvehicle engine is started manually after the vehicle has been secured tothe test deck, and the Maximum Throttle control is set so as to allowfor the initial acceleration of the engine as the dynamometer takes overfrom the manual operator. Let us suppose that the maximum throttlesetting is 9.9, representing nine tenths of maximum opening. As soon asthere is an input in the Required Road Speed line 6, i.e. according tothe setting of the source controls, whether tape, auto, or manual asdescribed hereinabove, there will be an error signal in line 2S. Thiserror will be large, and will bring about servo actuation of thethrottle to nine-tenths fully open, according to the limitation set bythe anode voltage of valve 24. At the same time, the potentiometer 28moves, and the resultant negative feedback ensures proper throttlesetting without hunting and also begins to restrain the throttle openingas the actual road speed rises.

The desired road speed varies, ofcourse, with time, as on the road, andthe feedback arrangement permits the apparatus to simulate true driverbehaviour in this respect, without chatter or hunting effects, bybringing back the throttle pedal after an initial excessive opening butbefore desired speed is actually attained. This control is applicable toany vehicle, irrespective of throttle characteristics, subject only tospan adjustment. The throttle opening can be arranged to reduce `at amoment when the actual speed is within a certain fraction of the desiredvalue, e.g. Subject to the Maximum Throttle setting, if the throttle isinsufficiently open, the servo will open it further, and the desiredroad speed program is accurately followed by the actual speed, withoutapplication of un-predetermined braking and without any direct throttleprogram.

FIGURES 3A and 3B illustrate by comparison the advantages to be gainedaccording to the present invention, by reference to the performance oftwo cars designated A and B. FIGURE 3A relates to the performance ofcars A and B on a prior art .dynamometer, while FIGURE 3B lrelates tocars A and B running on a dynamometer according to the invention. Thecar performances are described in respect of so-called events but itwill be appreciated that these may represent the stepwise sequencesinitiated by timed switchgear, or parts of a taped program consideredstepwise for clarity. Six events have been considered, as indicated atthe top of each iigure, timed according to the time scale of minutesalong the horizontal axes of the iigures. The same events apply to bothfigures.

In the upper part of each figure, the vertical scale representspercentage gradient applied, while the lower portions represent roadspeed attained in miles per hour.

FIGURE 3A relates to a dynamometer system in which speed and throttleposition are initially speciiied by the program, and an error signal isapplied to the gradient/ brake to correct the speed obtained by applyingload. Such a program is primarily designed to suit a particular car A;to apply it to another car B, the throttle opening must be standardisede.g. by iinding the opening ratio at 45 miles per hour for level roadspeed by experiment on the road, and then adjusting every throttleopening specihed for car B in the same ratio, by means of a special spanadjustment for throttle proportioning. This ratio is, however, not infact constant with speed, so that consequent errors are generated. Inthese iigures, car B is supposed to have approximately half the poweravailable in car A. This comparison depends on the degree of throttleopening, and the consequent ditferences in car behaviour are shownshaded (and magnied for clarity).

In FIGURE 3A the events are as follows:

Event 1.- Program: 4 minutes at 45 m.p.h.

Car A requires 0.3 throttle (the throttle openings are shown on thefigures against the identifying letters of the cars beside the relevantperformance curves, in tenths of full opening) but car B requires 0.6 asdetermined in the abovedescribed experiment.

Event 2.-Program: 6 minutes at 80 m.p.h. `Car A requires 0.45-throttleto reach 80 m.p.h.` in about 3 minutes and hold .that speed. Car B onthe other hand, given twice that amount of throttle opening according tothe determined ratio, calls for the application of braking load as shownat I to restrain acceleration at 80 m.p.h.

Event 3.-Pr0gram: 10 seconds at 35 m.p.h.

Car A and car B both have throttles fully closed as brake excitation isapplied and may decelerate together, but an error develops in Event 4.The brake application is denoted'by II.

Event 4.-Progntzm: 3 minutes at 35 m.p.h. Car A levels oit at 35 m.p.h.under 0.18 throttle, but with the calculated throttle of 0.36, car Bruns at a lower speed, giving an error shown at V. Y

Car A uses 0.5 throttle, but the corresponding use of 1.0 (full)throttle in car B is too high, and corrective. braking or gradient of10% is needed to keep the speed to 20 m.p.h. This gradient difference isshown at III.

Event 6.--Pr0grarm 6 minutelr at 35 m.p.h. (nio gradient) Car Acontinues at 0.5 throttle, accelerating to 35 m.p.h. as level ground isreached. Car B on the other hand, given a calculated full throttle again(see Event 5) needs brake application to keep the speed down to 35m.p.h. Moreover, the time required to do this must 'be found by trial.As soon as this point (x) on the time scale is reached, a fresh commandis given to car A of 0.18 throttle at 35 m.p.h."-

However, this will cause a speed error, as at 35 m.p.h. 0.36 is too lowfor car B. The brake error is shown at IV and the speed error at VI.

In FIGURE 3B the events are the same as far as intended program isconcerned, and both cars are the same. Similar adjustments are made tomatch the inertia of the cars by attaching weights to the rollsmechanism and lto match the windage and friction characteristics of thecars by adjusting the fan loading. The weight compensation controls areset so that a given brake or gradient signal is proportioned accordingto the weight of each car. In this case, however, the throttle iscontrolled according to the present invention. The cars now behave asfollows.

Event 1.-Prog1-am: 4 minutes wat 45 m.p.h.

The throttle is initially set at 1.0 with gradient at zero. Both carsrun too fast with full throttle and the system cancels the maximumthrottle and returns car A throttle to 0.3, car B throttle to 0.6,correct for 45 m.p.h. (see FIGURE 3B).

Event 2.-Program: 6 minutes at 80 m.p.h.

Initial throttle setting is 0.9 and both cars accelerate. As car Aapproaches m.p.h. the system reduces car AV throttle to 0.45, and car Bthrottle is reduced a little later to 0.8. Throttle reductions occur ator about point C in the diagram. Both cars are thereby held at 80 m.p.h.without brake signal alterations.

Event 3.--Progr:zm: 10 lseconds at 35 m.p.h.

Brake application with closed throttles brings both cars to 35 m.p.h.,decelerating together due to the weight proportioning device.

Event 4.-Pr0gram: 3 minutes at 35 m.p.h.

The initial throttle setting is raised to 1.0 with zero braking and thesystem reduces car A throttle to 0.18, and car B throttle to 0.4, inresponse to the fact that the de-y sired speed is the same as the speedattained already. No speed error occurs with car B.

Event 5.-Pr0gram: 6 minutes at Z0 m.p.h. up 71/2% gradient Event6.-Program: 6 minutes at 35 m.p.h.

Initial throttle is again 1.0, with zero gradient signal. Both carsaccelerate until they approach the desired speed until in theneighbourhood of point Cthe system returns the throttles to the sameultimate settings `as in Event 4.

It will be seen from the foregoing description that throughout 'a variedseries of events which are typical of actual road conditions thethrottle is subject to a control which is derived from the engine speedand is a function to the difference between that speed and the desiredspeed.

What I claim is:

1. In an apparatus 'for operating several throttle actuated stationaryvehicles having wheel systems mounted on traction rolls of a chassisdynamometer, the improvement which comprises means to generate a rstsignal representative of Ia predetermined wheel speed, means to generatesecond signals representative of the actual wheel speed of each vehicle,means to generate error signals representative of the difference betweensaid first and second signals, means to automatically and continuouslyapply said error signals to control the respective throttle of eachvehicle, means to generate a third signal representative of apredetermined gradient load, means to generate further signals bymodifying said third signal by respective factors equal to the weight ofeach of said vehicles and means to apply said further signals to controlthe respective resistive loads on the traction rolls of said chassisdynamometer for each of said vehicles.

2. In a method for operating a throttle-actuated stationary vehiclehaving a wheel system mounted on the traction rolls of a chassisdynamometer, the improvement which comprises generating a first signalrepresentative of a predetermined wheel speed,

generating a second signal representative of the 'actual wheel speed ofsaid vehicle,

comparing said signals and generating an error signal responsive to saidfirst and second signals,

generating a third signal representative of throttle position,

generating a second error signal responsive to said third signal andsaid first error signal, and

applying said second error signal to control the movement of saidthrottle.

3. In the method of claim 2, the improvement wherein said third signalreduces the throttle opening when said first error signal is within apredetermined range.

4. In the method of claim 2, wherein several of said first error signalsare generated to operate respective vehicles veach mounted on tractionrolls of a chassis dynamometer, the improvement which comprises-generating a fourth signal representative of a predetermined gradientload,

generating fifth signals by modifying said fourth signal by respectivefactors equal to the weight of each of said vehicles to control therespective resistive loads on the traction rolls of the chassisdynamometer for each of said vehicles.

5. In the method of claim 2, the improvement which comprises generatinga signal representative of a predetermined gradient load on said vehicleand applying said latter signal to control the resistive load n thetraction` rolls of said chassis dynamometer.

6. In the method of claim 2, wherein a fan is adapted to cool saidvehicle, the improvement which comprises operatively conveying energyfrom said dynamometer traction rolls to drive said fan.

7. In a method for operating a throttle-actuated stationary vehiclehaving a wheel system mounted on the traction rolls of a chassisdynamometer, the improvement which comprises generating a rst signalrepresentative of a predetermined wheel speed,

generating a second signal representative of the actual wheel speed ofsaid vehicle,

comparing said signals and generating an error signal representative ofthe difference between said signals, generating a third signalrepresentative of a predetermined maXimum-limit throttle position,

generating a fourth signal responsive to said third signal and saiderror signal,

generating a comparator balance signal representative of throttleposition,

generating a difference signal representative of the difference betweensaid fourth signal and said comparator balance signal, and

applying said difference signal to control the movement of saidthrottle.

8. In an apparatus having la throttle-actuated stationary vehicle with awheel system mounted on the traction rolls ofa chassis dynamometer, theimprovement which comprises means to generate a rst signalrepresentative of a predetermined wheel speed,

means to generate `a second signal representative of the actual wheelspeed of said vehicle,

means to generate an error signal representative of the differencebetween said first and second signals,

means to generate a third signal representative of a predeterminedmaximum limit throttle position, and means responsive to said errorsignal and said third signal to generate a fourth signal, and

means to apply said fourth signal to control the position of saidthrottle.

9. In an apparatus having a throttle-actuated stationary vehicle with awheel system mounted on the traction rolls of a chassis dynamometer, theimprovement which comprises means to generate a first signalrepresentative of a predetermined wheel speed,

means to generate a second signal representative of the actual wheelspeed of said vehicle,

means to generate an error signal representative of the differencebetween said first and second signals, means to generate a comparatorbalance signal representative of throttle position,

means to generate a difference signal representative of the differencebetween said error signal and said comparator balance signal, and

means to apply said difference signal to control the movement of saidthrottle.

I0. In the apparatus of claim 9, the improvement which comprises meansto generate a signal representative of a predetermined gradient load onsaid vehicle, and means to apply said latter signal to control theresistive load on the traction rolls of said chassis dynamometer.

11. In the apparatus of claim 9, the improvement wherein said means togenerate said comparator balance signal is adapted to lreduce thethrottle opening when said error signal is within a predetermined range.

12. In the apparatus of claim 9 wherein a fan is adapted to cool saidvehicle, the improvement which comprises means to operatively conveyenergy from said dynamometer traction rolls to drive said fan.

References Cited UNITED STATES PATENTS 2,248,938 7/1941 Bennett 73l172,883,975 4/1959 Spetner 12?:102 3,016,739 1/1962 Ionach et al 73-1163,050,994 8/1962 Heigl et al 73-118 X 3,099,154 7/1963 Vanderbilt 73-116OTHER REFERENCES Obert, E. G., Internal Combustion Engines, 2nd edition,1959, International Textbook Co., Scranton, Pennsylvania, page 48.

RICHARD C. QUEISSER, Primary Examiner.

J. W. MYRACLE, Assistant Examiner.

1. IN AN APPARATUS FOR OPERATING SEVERAL THROTTLE ACTUATED STATIONARYVEHICLES HAVING WHEEL SYSTEMS MOUNTED ON TRACTION ROLLS OF A CHASSISDYNAMOMETER, THE IMPROVEMENT WHICH COMPRISES MEANS TO GENERATE A FIRSTSIGNAL REPRESENTATIVE OF A PREDETERMINED WHEEL SPEED, MEANS TO GENERATESECOND SIGNALS REPRESENTATIVE OF THE ACTUAL WHEEL SPEED OF EACH VEHICLE,MEANS TO GENERATE ERROR SIGNALS REPRESENTATIVE OF THE DIFFERENCE BETWEENSAID FIRST AND SECOND SIGNALS, MEANS TO AUTOMATICALLY AND CONTINUOUSLYAPPLY SAID ERROR SIGNALS TO CONTROL THE RESPECTIVE THROTTLE